A conventional vehicle behavior data storing apparatus, which stores vehicle behavior data when vehicle behavior is determined to be abnormal, is disclosed in, for example, JP 2009-205368A. In this apparatus, the vehicle behavior is detected by various sensors and the vehicle behavior data indicating the detected vehicle behavior is compared with a reference value to check whether the detected vehicle behavior corresponds to occurrence of abnormal behavior of the vehicle.
Vehicle driving style (for example, manner of acceleration) differs from user to user, and hence vehicle behavior data indicating vehicle behavior generally differs among users. If the reference value, with which the vehicle behavior data is compared, is a fixed value, it is likely that the apparatus and the user recognize abnormality of vehicle behavior differently from each other. For example, although the apparatus determines that the vehicle behavior is abnormal, the user recognizes the same behavior to be not abnormal. In other cases, although the apparatus determines that the vehicle behavior is not abnormal, the user recognizes the same behavior to be abnormal. Because of difference in vehicle driving styles among users, a volume of the vehicle behavior data to be stored differs among the users. That is, the volume of vehicle behavior data to be stored increases as the apparatus determines that the vehicle behavior is abnormal more often. The volume of vehicle behavior data to be stored decreases as the apparatus determines that the vehicle behavior is abnormal less often.